1. Field of the Invention
The invention relates to voice interaction devices, and in particular, to an echo cancellation method utilizing different filters.
2. Description of the Related Art
FIG. 1 shows a conventional voice interaction device such as mobile phone, comprising a microphone 104 and speaker 102 simultaneously implemented. Remote signal #SRC received remotely, is amplified by the speaker 102 to provide local output #OUT. The microphone 104 receives local signal #MIX including vocal input #IN and environmental noise #ENV. The local output #OUT, however, may also be received by the microphone 104, inducing unwanted echo. Conventionally, an echo canceller 110 cancels the echo in local signal #MIX. The echo canceller 110 may be a FIR filter comprising a coefficient set learned from the remote signal #SRC, with the local signal #MIX filtered by the echo canceller 110 to eliminate the echo therein, generating a destination signal #DST for further transmission.
Vocal communication is typically performed in real time, making the performance of echo canceller 110 critical. The coefficient set in the echo canceller 110 is updated using normalized least mean square (NLMS) algorithm with a predetermined step size. As an example, a larger step size diverges the coefficient set faster, but renders a lower SNR filter result. Conversely, lower step size may render a quality destination signal #DST, but the speed may be insufficient for real-time communication. A tradeoff is thus presented between rapid convergence and fair filtering quality. Additionally, the local output #OUT, vocal input #IN may or may not simultaneously present. When both caller and recipient are talking, double talk is detected, and the performance of echo canceller 110 may decrease, generating noisy destination signal #DST. Thus, an enhanced echo cancellation method is desirable.